What does "step into the cut" mean?

“Tyrion. “Uncle! You’ll defend the honor of my realm, won’t you? You can ride the pig!”
The laughter crashed over him like a wave. Tyrion Lannister did not remember rising, nor climbing on his chair, but he found himself standing on the table. The hall was a torchlit blur of leering faces. He twisted his face into the most hideous mockery of a smile the Seven Kingdoms had ever seen. “Your Grace,” he called, “I’ll ride the pig . . . but only if you ride the dog!”
Joff scowled, confused. “Me? I’m no dwarf. Why me?”
Stepped right into the cut, Joff. “Why, you’re the only man in the hall that I’m certain of defeating!”

Excerpt From: George R.R. Martin. “A Storm of Swords.” Bantam. iBooks.

Hi. What does the underlined part mean?

Thank you.